“THIS IS JUST LIKE FINDING THEVENIN’S IMPEDANCE WHEN BOTH DEPENDENT AND INDEPENDENT SOURCE ARE PRESENT IN THE NETWORK “. So plz dont think this is different topic. This is one of the application of Thevenin Theorem….. 🙂

The method is also called E.M.F. method of determining the voltage regulation. The method requires following data to calculate the regulation.

_{a}).

**Open circuit characteristics**which is the graph of open circuit voltage against the field current. This is possible by conducting open circuit test on the alternator.

**Short circuit characteristics**which is the graph of short circuit current against field current. This is possible by conducting short circuit test on the alternator.

**1.O.C. Test:**

_{oc})

_{ph}against I

_{f}is plotted.

**Note**: This is called open circuit characteristics of the alternator, called O.C.C. This is shown in the Fig.

Fig. 2 O.C.C. and S.C.C. of an alternator |

**2. S.C.Test**

**straight line**graph passing through the origin while O.C.C. resembles B-H curve of a magnetic material.

**Note**: As S.C.C. is straight line graph, only one reading corresponding to full load armature current along with the origin is sufficient to draw the straight line.

**3. Determination of Impedance from O.C.C. and S.C.C.**

_{s }for any load and load p.f. conditions.

_{s}. The voltage responsible for driving this short circuit current is internally induced e.m.f. This can be shown in the equivalent circuit drawn in the Fig.

Fig. 3 Equivalent circuit on short circuit |

Z_{s }= E_{ph}/ I_{asc }

_{s}. So expression for Z

_{s }can be modified as

So O.C.C. and S.C.C. can be effectively to calculate Z_{s}.

**4. Regulation Calculations:**

From O.C.C. and S.C.C., Z_{s }can be determined for any load condition.

_{a}) can be measured by different methods. One of the method is applying d.c. known voltage across the two terminals and measuring current. So value of R

_{a }per phase is known.

So synchronous reactance per phase can be determined.

_{ph }can be determined by the mathematical expression derived earlier.

where V_{ph }= Phase value of rated voltage

I_{a }= Phase value of current depending on the load condition

cosΦ = p.f. of load

_{a }and X

_{s }values are known from the various tests performed.

The regulation then can be determined by using formula,

**5.Advantages and Limitations of Synchronous Impedance Method:**

**Advantage:**

_{s }for any load condition can be calculated. Hence regulation of the alternator at any load condition and load power factor can be determined.

**Limitation:**

**pessimistic method.**

Why is the sychronous impedance obtained higher than actual here?

What is the main difference between Emf method and mmf method to find voltage regulation?

Can The voltage regulation of an alternator by emf method be greater than 100%.

I need a reply bcz I have an exam tommorow.I would greatful for your help

no… voltage regulation cannot be 100%..

very precised one

🙂 🙂